This invention relates to a weft picking method and a device for carrying out the method in an air jet loom of the type wherein a weft yarn is carried by air jets from auxiliary nozzles in addition to an air jet from a weft inserting nozzle or main nozzle, and more particularly to an improvement in a method for ejecting air from the auxiliary nozzles to a weft guide channel defined by the almost closed circular sections of a plurality of air guide members.
Many methods for accomplishing weft picking by ejecting air from a plurality of auxiliary nozzles in addition to a weft inserting nozzle have been proposed in which there is a method wherein the weft picking is accomplished by carrying a weft yarn through a weft guide channel formed by a plurality of air guide members. Each air guide chamber is formed with a generally circular section which is almost closed except for a narrow slit, which circular section defines at its inner surface the above-mentioned weft guide channel, and therefore, such an air guide member is referred to as "a closed type air guide member".
The weft picking methods using the closed type air guide members can be classified into two categories. One of them is as follows: the inner surface of the circular section of the air guide member is tapered in the direction of the loom side which is opposite the weft inserting nozzle. With such air guide members, an air jet from the weft inserting nozzle is, after serving to pull the weft yarn to be picked out of the weft inserting nozzle, ejected into the weft guide channel formed by the circular section tapered inner surfaces of successively positioned air guide members, in order to form an air stream which gradually converges toward the aforesaid opposite loom side. In addition to this, auxiliary air jets are ejected from the auxiliary nozzles to assist the main air stream.
The other of the two method categories is as follows: the inner surface of the circular section of the air guide member is not tapered, in which an air jet from the weft inserting nozzle is, after serving to pull the weft yarn out the weft inserting nozzle, guided through the weft guide channel so that the guided air is dispersed through each alignment clearance formed between the adjacent air guide members. Thereafter, a portion of an air jet from an auxiliary nozzle is ejected through the alignment clearance of the row of air guide members into the weft guide channel to push the weft yarn against a side of the weft guide channel and then strike the inner surfaces of the circular sections of the air guide members to be deflected so as to guide the weft yarn to the vicinity of the succeeding auxiliary nozzle. Then, the succeeding auxiliary nozzle ejects an air jet to take over the weft yarn carrying action of the preceding auxiliary nozzle. Such weft yarn carrying action is taken over, in turn, by the further succeeding auxiliary nozzles to carry the weft yarn through the weft guide channel.
However, the above mentioned methods have encountered drawbacks in which the interference of the air jet from the weft inserting nozzle with the air jets from the auxiliary nozzles occurs at a transitional stage where the air ejection from the auxiliary nozzle starts, so that the air stream formed in the weft guide channel is unavoidably disturbed.
Specifically, in the above-mentioned former method wherein the main air stream through the weft guide channel is formed mainly by virtue of the air jet from the weft inserting nozzle, the head section of the air stream goes ahead of the leading end of the weft yarn to be picked and, therefore when an air jet from the first auxiliary nozzle (closest to the weft inserting nozzle) is angularly ejected from behind the air stream head section toward the head section of the air stream, the air stream head section is divided into two sections bounded by a location to which the air jet from the auxiliary nozzle strikes. The rear part of the air stream head section is pushed angularly forward and is thus accelerated, but the front section is slightly pulled backward and is thus decelerated. Accordingly, at the next step, both the front and rear sections of the divided air stream head section strike each other to generate a turbulence in the weft guide channel.
Also in the above-mentioned latter method wherein the air stream through the weft guide channel is formed mainly by virtue of the air jets from the auxiliary nozzles, the air jet from the weft inserting nozzle can reach the vicinities of the second and third auxiliary nozzles, and therefore an interference effect similar to that in the above-mentioned former method occurs. Additionally, in a range where the air stream from the weft inserting nozzle is sufficiently dispersed and the weft yarn carrying action is accomplished only by air jets from the auxiliary nozzles, when the air jet from the preceding auxiliary nozzle reaches the vicinity of the succeeding auxiliary nozzle, the intensity of the air jet from the preceding auxiliary nozzle has been lowered. At this state, when the succeeding auxiliary nozzle ejects an air jet at a high speed, the high speed air jet strikes the air jet (lowered in speed) from the preceding auxiliary nozzle to disturb the air stream in the weft guide channel. Such striking of the air jet from the succeeding auxiliary nozzle air against the air stream in the weft guide channel can not be avoided even by successively ejecting air jets from the auxiliary nozzles sufficiently prior to the air stream reaching the air jet from the succeding auxiliary nozzle.